Related Field
The present invention relates to a suction device for use in a papermaking machine. The suction device may be, for example, a moulding box intended for a through-air drying machine. The invention also relates to a papermaking machine that uses the inventive suction device.
Description of Related Art
In papermaking machines, various kinds of suction devices are used that act on fibrous webs through a fabric that is permeable to air and water. One use for such suction devices is as moulding boxes in through-air drying machines, i.e. TAD machines. In a TAD machine, a wet fibrous web is dried as it is carried over one or several TAD cylinders on a permeable fabric with an imprinting pattern. To imprint a three-dimensional patterns into the fibrous web that is manufactured, the web and the permeable fabric can made to pass a moulding box before the web is carried by the permeable fabric to the TAD cylinder or cylinders. The moulding box is a suction device that draws the fibrous web towards the permeable fabric as the web and the permeable fabric passes the moulding box. This causes the wet fibrous web to be drawn into the permeable fabric such that the pattern of the permeable fabric is imprinted into the wet fibrous web. The pattern which has been imprinted into the wet fibrous web will remain when the fibrous web has been dried. An example of a moulding box is disclosed in, for example, U.S. Pat. No. 5,718,806. The inventors of the present invention have noted that, in paper making machines using suction devices such as moulding boxes, there may be disturbances in the area downstream of the suction device and that this may sometimes be caused by the suction device itself. Therefore, it is an object of the present invention to provide an improved suction device that can be used, for example, as a moulding box in TAD machines.